The invention relates to a bar code reading device. The bar code reader comprises a semiconductor laser diode having a first end face. The first end face is optically coupled to an end of a section of an optical waveguide in order to scan the bar code provided on an object. The bar code reader also comprises a detector for detecting the radiation reflected by the bar code.
A device of this kind is described in U.S. Pat. No. 4,286,145. The light produced by the semiconductor laser diode is coupled into an optical waveguide. The light is used to read the bar code provided on a surface of an object, for example a retail sales item. During reading, the light is either reflected or not, depending on the pattern of the bar code information. The reflected light is coupled into the optical waveguide, separated by a directional coupler, and received by the detector. The detector detects the content of the bar code from the reflected light and converts this information into a binary electrical signal which is input to a data processing system.
Devices of this kind are usually used in retail sales outlets. This is because most retail sales items are provided with a UPC (Universal Product Code) bar code, enabling operations such as totaling sales prices, recording inventories, etc. to be more efficiently performed.
It is a drawback of the known device, however, that a directional coupler is used for separating the transmitted radiation and the reflected radiation. Such a directional coupler is expensive and absorbs a part of the energy of the reflected light. Because only the reflected light contains the information read, this loss of energy means that the energy of the transmitted light must be high. For use in sales outlets, safety regulations limit the maximum energy permissible.